netdev - Re: [PATCH net-next] net: phy: qcom: qca808x: Add .get_rate

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Message-ID: <aMgootkPQ/GcdiXX@oss.qualcomm.com>
Date: Mon, 15 Sep 2025 20:24:26 +0530
From: Mohd Ayaan Anwar <mohd.anwar@....qualcomm.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: andrew@...n.ch, Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: phy: qcom: qca808x: Add .get_rate_matching
 support

On Mon, Sep 15, 2025 at 01:09:39PM +0100, Russell King (Oracle) wrote:
> This shows that the PHY supports SGMII (4) and 2500base-X (23). However,
> as we only validate 2500base-X, this suggests stmmac doesn't support
> switching between SGMII and 2500base-X.
> 
> What *exactly* is the setup with stmmac here? Do you have an external
> PCS to support 2500base-X, or are you using the stmmac internal PCS?

Internal PCS. But it's not really pure 2500base-X...
I found an older thread for this exact MAC core [0], and it looks like
we have an overclocked SGMII, i.e., 2500base-X without in-band
signalling.

Just wondering if registering a `.get_interfaces` callback in
`dwmac-qcom-ethqos.c` and doing something like the following will be
helpful?

case PHY_INTERFACE_MODE_2500BASEX:
	__set_bit(PHY_INTERFACE_MODE_2500BASEX, interfaces);
	fallthrough;
case PHY_INTERFACE_MODE_SGMII:
	__set_bit(PHY_INTERFACE_MODE_SGMII, interfaces);
	break;
...

This should ensure that both SGMII and 2500base-X are validated,
allowing switching between them.

	Ayaan
---
[0] https://lore.kernel.org/netdev/4f642463-3a8c-4412-a007-42fb65c4276e@lunn.ch/